The present invention relates to the analysis of sample, in particular the detection of bones in meat.
In the production of meat the occurrence of bones is a particular concern. This concern is greatest in processed meat where the consumer expects that all the bones have been removed and the final product is fit for safe human consumption. Chicken processing is especially concerned with bone contamination. The bones in chicken meat are softer than those in beef or pork and often can be left undetected in the final product. The processes applied to the detection of bones in meat can equally be applied to like sample analysis problems.
At present the only reliable technique for the automatic detection of bones in meat is that using x-ray technology, although other wavelengths of electromagnetic radiation have been tried. Accordingly, the description of this invention will be made in the context of x-ray scanning. However, it is applicable to other scanning methods.
An example of a typical x-ray system for the on-line detection of bones in meat is shown in FIG. 1. In this system the meat (10) passes along a conveyor belt (12) and underneath the output from an x-ray tube (14). Underneath the conveyor belt (12) is an x-ray sensor (16) which is typically a linear series of photodiodes transverse to the direction of the conveyor belt (12) which are covered with a scintillating material to convert the x-rays to light. As the meat (10) passes along the conveyor (12) the photodiodes are read out on a line by line basis thus building up a two dimensional image. The width of the image is fixed by the number of photodiode elements and the height of the image variable. The processing of the signal coming back from the photodiodes can be achieved on a line by line basis but more sophisticated processing can be achieved by building up the lines into a two dimensional frame.
Once a frame of data has been acquired signal processing techniques can be applied to the frame in order to determine the presence of a contaminant such as a bone. The simplest technique is to apply a greyscale threshold across the whole of the image obtained and to make the decision as to whether the image contains a bone/contaminant or not on the basis of whether a predetermined threshold is exceeded. Such a technique works well for products which are perfectly homogeneous and for which the likely contaminant absorbs x-rays much greater than the surrounding food medium. Such techniques are not robust for products which are not homogenous or for which the x-ray absorbtion of the defect is very close to that of the background food product. Techniques to overcome this difficulty rely on forming the meat product into a homogenous block or by floating the product in water in order to try to normalise out the meat thickness variations. Such techniques are not widely used because of hygiene and other practical meat handling considerations.
In order to overcome the limitations of simple global thresholding a number of two dimensional image processing algorithms have been developed for the detection of contaminants in x-ray images. Such techniques are dynamic entropic thresholding, morphological detection algorithms, neural network based algorithms and texture based techniques. These methods are all based on the fact that the defect (bone or other contaminant) will absorb more x-rays than the background food medium and therefore will locally appear darker in the image. These techniques are well described in the literature.
Usually such algorithms are applied to the greylevel image and result in a binary image representing those regions of the image where the defect has been segmented. In simple applications such greyscale segmentation techniques are sufficient for the isolation of any bone or other contaminants.
In many meat inspection applications such processing is not sufficient for the isolation of just the bones/contaminants since pieces of meat folded over will look just like a bone and therefore lead to a false rejection. One technique of overcoming such a difficulty is to take a number of features of the image portion which has been segmented by the greyscale segmentation algorithm. Such features could be based on the size and shape of the binary image portion and the grey level statistics of the image portion in the original grey level image. Given a large number of features obtained from bone and non bone data training sets, a pattern classification scheme could be designed to differentiate between the bone and non bone segmented image portions. Such classification schemes are commonly implemented with neural networks and in particular the Multi Layer Perceptron (MLP) network trained with a back propagation learning rule.
The system of FIG. 1 includes a neural network analysis which can automatically find bones in x-ray images of chicken meat. The image acquired from the x-ray sensor (16) is sent to a PC (18) for analysis. Morphological analysis reveals those areas where bones are likely to occur and the subsequent neural network algorithms indicate those areas which are genuine bones from those which are false rejections.
There are difficulties with such an approach. In particular, the meat varies over time due to seasonal variations, bird breed types, processing changes etc. and the x-ray sensor suffers from long term radiation damage. The present invention seeks to alleviate these.
The present invention therefore provides an apparatus comprising a source of penetrating radiation, a detector for that radiation, a sample container, and a stage between the source and the detector for supporting the sample container, wherein the sample container includes a data storage element and the apparatus includes a reader for that data storage element, the reader being connected to a control means adapted to control the apparatus on the basis of the content of the data storage element. Thus, by including information in the data storage element relating to the nature of the sample, the apparatus can be tuned to that type or class of sample and more reliable results obtained. Since the data is stored in the sample container, the process can be automated, there is no confusion as to the correct data set for a given sample and no need to time the arrival of data sets in correlation with the arrival of samples.
It will be preferred that the penetrating radiation is X-radiation but as noted above the invention is applicable to other scanning processes.
A suitable data storage element is a bar code, and a suitable sample container is a tray. These are particularly simple items to manufacture and store. The data can be encoded in the bar code, for example as a digital code. The tray is preferably open topped to allow easy access for filling and inspection.
A parameter of the apparatus that can be controlled is the source power. Some samples require a higher power in order to resolve internal detail, whereas other samples may be typically thinner and hence require lower power. This aspect of the invention therefore allows greater accuracy by avoiding the need to select a compromise power level.
The apparatus preferably includes an image storage means for storing the output of the detector, wherein the data storage includes an identification code for a sample in the container, the image storage means being adapted to store the detector output in association with the identification code. This enables a number of useful processes as will be explained.
Where the detector is a solid state device whose output can be obtained in real time, an analysis means for analysing the detector output can be incorporated in order to determine the content of the sample. A suitable analysis means for this type of work is a neural network. This can be trained to the specific type of work, and a plurality of analysis means could be provided, each for use in relation to a particular class of samples. In most cases, the analysis means will be in the form of software and a plurality thereof can most easily be provided by storing at least two sets of parameters for use in relation to the software. Thus, an analysis means can be selected by the control means according to the content of the data storage means, enabling still further or alternative improvements in accuracy.
In general, at least part of the samples will be presented for checking in association with the stored detector output. These will usually be the samples where the apparatus has detected an error or fault. There will preferably be a feedback means for training the neural network after inspection of that sample by an operator. Preferably, a location feedback device such as a touch screen monitor is provided. This enables the inspection staff to indicate the location of an error that has been missed by the system. Image features of the error can then be generated and fed back to the neural network training program. This enables more accurate training since the algorithm does not have to guess where the error is located.
The apparatus set out above is particularly useful in scanning meat for bones. Containers in which the apparatus detects a bone are then presented for checking, and the stored detector output can be displayed to assist the operator. It is preferred that the stored detector output is displayed and the location of the bone in the container is identified.
In the use of this apparatus to scan deboned meat, the plurality of analysis means when provided will most usefully be adapted to detect bones in meat originating from different areas of a carcass, such as chicken breast, chicken wing, and chicken leg. These different areas have different weights, thicknesses, absorptions etc and the ability to set a different power level and apply a different program is highly advantageous in improving accuracy.